BERN (Reuters) - Britain's Chris Froome seems to be heading for a third Tour de France title seemingly unchallenged as rivals fail to unsettle his well-oiled Team Sky machine but try telling him that.

Monday's headline in French sports daily L'Equipe claimed he was 'Sans Rival' (without a rival) with one block of racing in the Alps left before Sunday's parade to the Champs Elysees.

Colombian Nairo Quintana (Movistar), runner-up to Froome in 2013 and 2015, has been promising attacks but has been toothless so far and the other big names just do not seem strong enough.

Frenchman Thibaut Pinot and Alberto Contador, who could have shaken Froome, both pulled out of the race, because of illness and injury respectively, leaving the Briton firmly in control.

But Froome has rubbished suggestions he has no rivals for the title ahead of what he described as four "very tricky" days.

"I don't agree, I think other teams have said they're going to attack this week in the Alps and I expect they will do," he said after 'ticking off' Monday's 16th stage, a mostly flat ride from Moirans-en-Montagne.

"To say the Tour is won and I have no rival is rubbish," he added. "A lot can happen in four days, all you need is one bad day in the mountains and you can lose minutes."

After Tuesday's rest day, the Tour heads into the Alps with a mountain-top finish at Finhaut-Emosson, Swizterland, an uphill time trial on Thursday, another summit finish on Friday and a final mountain trek on Saturday.

"In this next block of four very tricky days, each day has its own challenges. The time trial is very important, each day is extremely challenging," said Froome.